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Session Q06 - DCP: COMPLEXITY AT INTERFACES: X-RAY SCATTERING STUDIES AT INTERFACES
Mixed session, Friday morning, March 24, 8:00
Ballroom A3, San Jose Convention Center
An x-ray scattering study is presented of the orientational phase diagram of silicon surfaces for orientations between [114] through [113] to [5\hspace0.02in5\hspace0.02in12] and for temperatures between 300 and 1500 K. For surfaces with positive misorientation angles (towards [001]), at the highest temperatures, the surface is uniformly stepped. Remarkably, in this single phase region, strongly temperature dependent diffuse scattering is found, reminiscent of critical scattering. The diffuse scattering is a result of step fluctuations and foreshadows a faceting transformation occuring below T_t = 1223 K, at which the surface phase-separates into (113) facets in coexistence with the stepped phase. The faceting transformation found here is very different from those previously observed, where faceting is induced by a first-order transformation between different surface phases, such as reconstructed and unreconstructed phases. In contrast, our results suggest that the faceting of stepped Si(113) surfaces is a consequence of a direct attractive interaction between steps. T_t may be identified as a tricritical point. For temperatures between a triple point at T_3 = 1134 K and 300 K, coexistence between (113) facet and the (114) facet is found. For surfaces with negative misorientation angles (towards [111]), the orientational phase behavior is found to be qualitatively similar with tricritical diffuse scattering anticipating another tricritical point at T_t^\prime = 1200 K, and another triple point at T_3^\prime = 1180 K. Below T_3^\prime , coexistence between (113) facet and (5\hspace0.02in5\hspace0.02in12) facet is found. This work was performed in collaboration with S. G. J. Mochrie and M. Yoon and supported by NSF (DMR 9119675) and JSEP (DAAL-03-94-C-0001).